This is a Shannon Award providing partial support for research projects that fall short of the assigned institute's funding range but are in the margin of excellence. The Shannon award is intended to provide support to test the feasibility of the approach; develop further tests and refine research techniques; perform secondary analysis of available data sets; or conduct discrete projects that can demonstrate the PI's research capabilities or lend additional weight to an already meritorious application. The abstract below is taken from the original document submitted by the principal investigator. Development of breast and ovarian epithelial carcinomas in humans is associated with frequent loss of heterozygocity, suggesting the involvement of multiple tumor suppressor genes. Newly identified breast (and ovarian) cancer gene (BRCA1) was found mutated/deleted in a small percentage of inherited but not common in sporadic tumors. Several tumor suppressor genes such as p53 and MTS1&2 have been investigated for their roles in breast and ovarian cancers, but the principal breast/ovarian tumor suppressor gene(s) has yet to be identified. In studying growth regulation, we have recently identified and cloned the complete murine cDNA for a 96 kd, mitogen-responsive protein, referred to as mDab. A 782 bp human cDNA fragment (DOC-2), which is nearly identical to the murine sequence of mDab, was isolated by Mok and co- workers in an attempt to identify tumor suppressor genes. It was found that mDab (DOC-2) was expressed in normal ovarian epithelial cells, but its expression was consistently absent in ovarian carcinoma cell lines, as well as tumor tissues. mDab is rapidly serine-phosphorylated upon serum or growth factor stimulation, and is associated with Fyn kinase in vitro. The structural features of mDab also suggest a signalling role: mDab contains a non-SH2 phosphotyrosine interaction domain (PID) and proline-rich SH3 binding motifs. Additionally, in our preliminary studies, mDab was found to exhibit growth regulating/suppressing activity in macrophages and PC12 cells, and was absent in several breast carcinoma cell lines. This study will test the hypothesis that mdab (DOC-2) is a tumor suppressor gene of breast and ovarian epithelial carcinomas by two criteria: 1) growth suppressing activity, and 2) altered expression, mutation, and/or deletion in cancer cells. Sense and antisense expression of mDab will be used to re-introduce mDab expression in cancer cells and suppress expression in non-cancer epithelial cells. Following alteration of mDab expression, the cells will be tested in tissue cultures for growth, soft-agarose plates for colony formation, and nude mice for tumorigenicity. The altered expression, mutation, and deletion of mDab will be investigated in breast and ovarian cancer cells, using approaches such as Western and Northern blotting, restriction fragment length polymorphism, and DNA cloning/sequencing. The current studies will provide basis for diagnostic and therapeutic approaches.